Mask blank, transfer mask, and method for manufacturing semiconductor device

ABSTRACT

A mask blank including a light shielding film pattern having high ArF light fastness. 
     The light shielding film is on a transparent substrate. In the mask blank, the light shielding film is a single layer film formed of a material containing silicon and nitrogen, and the light shielding film has an optical density to an ArF excimer laser exposure light of 2.5 or more, a surface reflectance to the exposure light of 40% or less, a back-surface reflectance to the exposure light of 40% or less, a transmittance to a light having a wavelength of 900 nm of 50% or less, an extinction coefficient to a light having a wavelength of 900 nm of 0.04 or more, and a thickness of 60 nm or less.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/327,172, filed Feb. 21, 2019, which is the U.S. National Stage ofInternational Application No. PCT/JP2017/028043, filed Aug. 2, 2017,which claims priority to Japanese Patent Application No. 2016-165550,filed Aug. 26, 2016, the entire contents of which are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a mask blank and a transfer maskmanufactured using the mask blank. Additionally, the present disclosurerelates to a method of manufacturing a semiconductor device using thetransfer mask.

BACKGROUND ART

At steps in manufacturing a semiconductor device, a photolithographymethod is used to form a fine pattern. To make a semiconductor devicepattern finer, it is necessary not only to make a mask pattern formed ona transfer mask finer, but also to shorten a wavelength of an exposurelight source used in photolithography. In recent years, an ArF excimerlaser (wavelength: 193 nm) has been applied increasingly to an exposurelight source used in manufacturing a semiconductor device.

The transfer mask includes a binary mask. For example, the binary maskis a transfer mask including a light shielding film pattern configuredto shield exposure light and formed on a transparent substrate, asdescribed in Patent Literature 1. As the light shielding film, achromium (Cr)-based or molybdenum silicide (MoSi)-based material hasbeen widely used.

When a light shielding film includes a chromium-based material, a mixedgas of chlorine-based gas and oxygen gas is used in dry etching. Thismixed gas is highly radical, and thus it has been difficult to dry etchthe light shielding film with sufficient anisotropy, and it has beendifficult to form a fine light shielding film pattern with sufficientprecision.

When a molybdenum silicide (MoSi)-based material is used as a materialfor the light shielding film, the aforementioned problem with dryetching is less likely to occur, and it is easy to form a fine lightshielding film pattern with high precision. On the other hand, anMoSi-based film has been recently found to have low fastness to exposurelight of an ArF excimer laser (ArF exposure light) (that is, ArF lightfastness).

CITATION LIST Patent Literature

-   Patent Literature 1: JP 2007-33470 A

SUMMARY OF DISCLOSURE Technical Problem

When a material containing silicon and nitrogen is used as a phase shiftfilm, it is confirmed to achieve high ArF light fastness. Thus, theinventors have found a possibility that a thin film (SiNx film) made ofthe material containing silicon and nitrogen can be applied as a lightshielding film of a binary mask to obtain high ArF light fastness, andthe inventors have studied the light shielding film. However, when thelight shielding film is formed using an SiNx film with a single layerstructure, the following problem has been found.

In a binary mask, a light shielding film formed a transfer pattern istypically required to have an optical density of equal to or more than apredetermined value (e.g., 2.5 or more) to an ArF excimer laser exposurelight (hereinafter referred to as ArF exposure light) with which anexposure apparatus irradiates. Further, the light shielding film isrequired to have a reflectance of equal to or less than a predeterminedvalue for ArF exposure light entering a surface on a side being incontact with a transparent substrate (back-surface reflectance, forexample, 40% or less), and at the same time, is required to have areflectance of equal to or less than a predetermined value to ArFexposure light entering a surface on a side opposite to a transparentsubstrate side (surface reflectance, for example, 40% or less). From theviewpoint of an optical density required for the light shielding film,the SiNx film preferably contains a smaller amount of nitrogen. However,from the viewpoint of a surface reflectance and a back-surfacereflectance required for the light shielding film, the SiNx film needsto contain a certain amount of nitrogen.

Depending on an exposure apparatus, an operation involving exposure maybe performed after alignment mark detection using long-wavelength lighthaving a wavelength of 800 nm or more and 900 nm or less. Here, thislong-wavelength light is referred to as long-wavelength detection lightLW. When a binary mask including, as a light shielding film, an SiNxfilm with a single layer structure is placed in an exposure apparatususing the long-wavelength detection light LW to perform exposure, aproblem of an exposure operation that cannot be performed owing toinsufficient detection sensitivity in alignment mark detection has oftenoccurred.

When the nitrogen content of the SiNx film constituting the lightshielding film is largely decreased, a transmittance of thelong-wavelength light can be decreased, and the problem of insufficientdetection sensitivity in alignment mark detection is solved. However,since both a surface reflectance and a back-surface reflectance to ArFexposure light of such a light shielding film increase, another problemof a large decrease in transfer performance as the binary mask occurs.

An object of the present disclosure is to provide a mask blank includinga light shielding film including an SiNx film with a single layerstructure, and the mask blank satisfies various optical properties forArF exposure light required for a light shielding film, and also solvesa problem of insufficient sensitivity during mark detection performedusing long-wavelength light having a wavelength of 800 nm or more and900 nm or less. Additionally, another object of the prevent disclosureis to provide a transfer mask manufactured using such a mask blank.Further, still another object of the present disclosure is to provide amethod of manufacturing a semiconductor device using such a transfermask.

Solution to Problem

To solve the aforementioned problems, the present disclosure includesthe following configurations.

Configuration 1

A mask blank including a light shielding film on a transparentsubstrate, wherein the light shielding film is a single layer filmformed of a material containing silicon and nitrogen, and the lightshielding film has an optical density to an ArF excimer laser exposurelight of 2.5 or more, a surface reflectance to the exposure light of 40%or less, a back-surface reflectance to the exposure light of 40% orless, a transmittance to a light having a wavelength of 900 nm of 50% orless, an extinction coefficient k to a light having a wavelength of 900nm of 0.04 or more, and a thickness of 60 nm or less.

Configuration 2

The mask blank according to configuration 1, wherein the light shieldingfilm is formed of a material consisting of silicon and nitrogen, or amaterial consisting of silicon, nitrogen, and one or more elementsselected from a semimetal element and a non-metal element.

Configuration 3

The mask blank according to configuration 1 or 2, wherein the lightshielding film includes at its surface layer a composition gradientportion with increased oxygen content toward a surface opposite to thetransparent substrate, and the light shielding film except for thesurface layer is formed of a material consisting of silicon andnitrogen, or a material consisting of silicon, nitrogen, and one or moreelements selected from a semimetal element and a non-metal element.

Configuration 4

The mask blank according to any one of configurations 1 to 3, includingon the light shielding film a hard mask film made of a materialcontaining chromium.

Configuration 5

A transfer mask including on a transparent substrate a light shieldingfilm including a transfer pattern, wherein the light shielding film is asingle layer film formed of a material containing silicon and nitrogen,and the light shielding film has an optical density to an ArF excimerlaser exposure light of 2.5 or more, a surface reflectance to theexposure light of 40% or less, a back-surface reflectance to theexposure light of 40% or less, a transmittance to a light having awavelength of 900 nm of 50% or less, an extinction coefficient k to alight having a wavelength of 900 nm of 0.04 or more, and a thickness of60 nm or less.

Configuration 6

The transfer mask according to configuration 5, wherein the lightshielding film is formed of a material consisting of silicon andnitrogen, or a material consisting of silicon, nitrogen, and one or moreelements selected from a semimetal element and a non-metal element.

Configuration 7

The transfer mask according to configuration 5 or 6, wherein the lightshielding film includes at its a surface layer a composition gradientportion with increased oxygen content toward a surface opposite to thetransparent substrate, and the light shielding film except for thesurface layer is formed of a material consisting of silicon andnitrogen, or a material consisting of silicon, nitrogen, and one or moreelements selected from a semimetal element and a non-metal element.

Configuration 8

A method of manufacturing a semiconductor device, the method includingthe step of exposure-transferring a transfer pattern on a resist film ona semiconductor substrate using the transfer mask according to any oneof configurations 5 to 7.

Advantageous Effects of Disclosure

A light shielding film of a mask blank of the present disclosure isformed of a material containing silicon and nitrogen, and has atransmittance to a light having a wavelength of 900 nm of 50% or lessand an extinction coefficient k to a light having a wavelength of 900 nmof 0.04 or more. The material containing silicon and nitrogen has highArF light fastness. Additionally, the material containing silicon andnitrogen has properties in which the transmittance becomes higher andthe extinction coefficient k becomes smaller to a light having awavelength of 800 nm or more and 900 nm or less as the wavelength of thelight becomes longer. Owing to these optical properties, when atransmittance to a light having a wavelength of 900 nm is 50% or lessand an extinction coefficient to a light having a wavelength of 900 nmis 0.04 or more, long-wavelength detection light LW can be decreasedsufficiently. Therefore, the long-wavelength detection light LW can beused to detect with sufficient contrast an alignment mark formed on atransfer mask manufactured using this mask blank, and a problem ofexposure that cannot be performed owing to insufficient detectionsensitivity in alignment mark detection can be solved.

Additionally, the light shielding film of the mask blank of the presentdisclosure has an optical density to an ArF excimer laser exposure lightof 2.5 or more, a surface reflectance to the exposure light of 40% orless, and a back-surface reflectance to the exposure light of 40% orless. Thus, the light shielding film has an optically sufficienttransfer property by exposure for pattern exposure light.

Further, the light shielding film has a film thickness of 60 nm or less,and thus a bias (EMF bias) involved in an electromagnetic field effectof a mask pattern and a shadowing effect caused by a mask pattern stereostructure can fall within the allowable range. Additionally, the lightshielding film is a thin film, and thus it is easy to form a fine lightshielding film pattern.

Additionally, the light shielding film is a single layer, and thus thenumber of steps in manufacturing the light shielding film is small, andcontrol of manufacturing quality including a defect is facilitated.

Additionally, in the transfer mask of the present disclosure, a lightshielding film including a transfer pattern has the same properties asthe properties of the light shielding film of the mask blank of thepresent disclosure. In such a transfer mask, the light shielding filmincluding a transfer pattern has high ArF light fastness, andadditionally, a problem of exposure that cannot be performed owing toinsufficient detection sensitivity in alignment mark detection can besolved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating a configuration of a maskblank according to an embodiment of the present disclosure.

FIG. 2 is a graph of properties showing wavelength dependence of atransmittance of a light shielding film according to the embodiment ofthe present disclosure.

FIG. 3 is a graph of properties showing wavelength dependence of anoptical coefficient of the light shielding film according to theembodiment of the present disclosure.

FIG. 4A to 4F are cross-sectional views illustrating steps inmanufacturing a transfer mask according to an embodiment of the presentdisclosure.

DESCRIPTION OF EMBODIMENTS

First, the circumstances leading to the completion of the presentdisclosure will be described. The present inventors have intensivelystudied a cause of insufficient detection sensitivity in alignment markdetection using long-wavelength detection light LW. As a result, theinventors have found that insufficient detection sensitivity inalignment mark detection is due to insufficient optical contrast, andthis insufficient optical contrast is caused by a light shielding filmincapable of sufficiently decreasing the long-wavelength detectionlight.

Then, the inventors have studied a light shielding film capable ofsufficiently decreasing the long-wavelength detection light LW. In thestudy, the inventors have taken into consideration that the lightshielding film can be applied even when a wavelength of thelong-wavelength detection light LW varies depending on an exposureapparatus.

When the wavelength of a light is 800 nm or more and 900 nm or less, amaterial having high ArF light fastness and containing silicon andnitrogen has a higher transmittance as the wavelength of the lightbecomes longer. In other words, the material has spectral properties inwhich as the wavelength is longer, an extinction coefficient k issmaller. Then, a transmittance of the light shielding film at awavelength of 900 nm is specified to impart a property of sufficientlydecreasing the long-wavelength detection light LW to the light shieldingfilm. In view of such circumstances, the inventors have considered thata light shielding film can be formed of a material containing siliconand nitrogen and a transmittance of the light shielding film at awavelength of 900 nm can be specified to secure high ArF light fastnessand also to solve the problem of alignment mark detection failure.

Additionally, an optical density to ArF exposure light of the lightshielding film, a reflectance of each of a surface and a back-surface ofthe light shielding film to the exposure light, and a film thickness ofthe light shielding film are specified to enable transfer of a finepattern.

The inventors have further investigated the light shielding film, and asa result, found that a single layer film facilitating control of qualityincluding a defect and control of manufacturing steps with the decreasednumber of steps can be used to obtain a film satisfying theaforementioned specifications. As a result, the present disclosure hasbeen completed.

Mask Blank

Next, each embodiment of the present disclosure will be described. FIG.1 is a cross-sectional view illustrating a configuration of a mask blank100 according to an embodiment of the present disclosure. The mask blank100 illustrated in FIG. 1 includes a structure where a light shieldingfilm 2 and a hard mask film 3 are layered in this order on a transparentsubstrate 1.

Transparent Substrate

The transparent substrate 1 can be formed of synthetic quartz glass,quartz glass, aluminosilicate glass, soda-lime glass, low thermalexpansion glass (SiO₂—TiO₂ glass, or the like), or the like. Amongthese, synthetic quartz glass has a high transmittance to ArF exposurelight (wavelength: 193 nm) and is particularly preferable as a materialforming a transparent substrate of a mask blank.

Light Shielding Film

The light shielding film 2 is a single layer film formed of a materialcontaining silicon and nitrogen, and preferably a single layer filmformed of a material consisting of silicon and nitrogen or a materialconsisting of silicon, nitrogen, and one or more elements selected froma semimetal element and a non-metal element.

The light shielding film 2 contains no transition metal that can becomea factor of decreasing light fastness to ArF exposure light.Additionally, since there is no ruling out a possibility that the metalelement might become a factor of decreasing light fastness to the ArFexposure light, it is desirable that the light shielding film 2 containno metal element other than a transition metal.

The light shielding film 2 may contain any semimetal element in additionto silicon. Among the semimetal elements, the light shielding film 2preferably contains one or more elements selected from boron, germanium,antimony, and tellurium, and in this case, an increase in conductivityof silicon used as a sputtering target can be expected.

The light shielding film 2 may contain any non-metal element in additionto nitrogen. Here, the non-metal element in the present disclosureincludes a narrowly-defined non-metal element (nitrogen, carbon, oxygen,phosphorus, sulfur, and selenium), halogen, and the noble gas. Among thenon-metal elements, the light shielding film 2 preferably contains oneor more elements selected from carbon, fluorine, and hydrogen. Theoxygen content of the light shielding film 2 except for a region of asurface layer described below is preferably 5 atom % or less, and morepreferably 3 atom % or less. It is further preferable that the lightshielding film 2 except for the region of the surface layer do notpositively contain oxygen (at a detection lower limit value or less asmeasured by composition analysis using X-ray Photoelectron Spectroscopy(XPS)) or the like. This is because when a film made of a siliconnitride-based material contains oxygen, a value of the extinctioncoefficient k becomes small, and a sufficient light shielding propertyis less likely to be obtained.

For the transparent substrate 1, a material containing SiO₂ such assynthetic quartz glass as a main component is preferably used. When thelight shielding film 2 contains oxygen, the difference betweencomposition of the light shielding film 2 and composition of thetransparent substrate 1 becomes small, and there also occurs a problemof etching selectivity for the transparent substrate 1 that becomes lesslikely to be obtained in dry etching with fluorine-based gas performedin formation of a pattern on the light shielding film 2.

The light shielding film 2 may contain a noble gas. The noble gas is anelement existing in a film forming chamber when a thin film is formed byreactive sputtering and accordingly being capable of increasing adeposition rate to improve productivity. The noble gas becomes plasmaand collides with a target. As a result, a target constituent particleis emitted from the target. While the target constituent particle isemitted from the target, the target constituent particle incorporates areactive gas, and is layered on the transparent substrate 1 to form thethin layer. The noble gas in the film forming chamber is slightlyincorporated until the target constituent particle is adhered to thetransparent substrate 1 after the target constituent particle is emittedfrom the target. Preferable examples of the noble gas necessary for thereactive sputtering include argon, krypton, and xenon. Additionally, torelax a stress of the thin film, helium and neon having a small atomicweight can be incorporated positively in the thin film.

The nitrogen content of the light shielding film 2 is preferably 50 atom% or less, and more preferably 45 atom % or less. This is because whenthe nitrogen content is more than 50 atom %, the extinction coefficientsto ArF exposure light and for the long-wavelength detection light LWbecome small, and it becomes difficult to sufficiently shield light anddecrease light. Additionally, the nitrogen content of the lightshielding film 2 is preferably 25 atom % or more, and more preferably 30atom % or more. This is because when the nitrogen content is less than25 atom %, cleaning durability is likely to become insufficient, andadditionally, oxidation is likely to occur, and stability over time of afilm is likely to be impaired.

Additionally, the silicon content of the light shielding film 2 ispreferably 50 atom % or more, and more preferably 55 atom % or more.This is because when the silicon content is less than 50 atom %, theextinction coefficients to ArF exposure light and for thelong-wavelength detection light LW become small, and it becomesdifficult to sufficiently shield light and decrease light. Additionally,the silicon content of the light shielding film 2 is preferably 75 atom% or less, and more preferably 65 atom % or less. This is because whenthe silicon content is more than 75 atom %, cleaning durability islikely to become insufficient, and additionally, oxidation is likely tooccur, and stability over time of the film is likely to be impaired.

The light shielding film 2 is preferably formed of the materialcontaining silicon and nitrogen. Note that the noble gas is an elementdifficult to detect even by performing composition analysis such asRutherford Back-scattering Spectrometry (RBS) and XPS of the thin film.However, as described above, when the light shielding film 2 is formedby reactive sputtering, the noble gas is slightly incorporated.Therefore, the aforementioned material containing silicon and nitrogencan be considered to include a material containing the noble gas.

The light shielding film 2 is required to have a thickness of 60 nm orless. When the light shielding film 2 has a thickness of 60 nm or less,a bias (EMF bias) involved in an electromagnetic field effect of a maskpattern and a shadowing effect caused by a mask pattern stereo structurecan fall within the allowable range. Additionally, the light shieldingfilm 2 is relatively thin, and thus it becomes easy to form a fine lightshielding film pattern. The thickness of the light shielding film 2 ismore preferably 58 nm or less.

On the other hand, the thickness of the light shielding film 2 ispreferably 40 nm or more, and more preferably 45 nm or more. When thethickness of the light shielding film 2 is less than 40 nm, it becomesdifficult to secure the following optical density to ArF exposure light,and it also becomes difficult to obtain a property of sufficientlydecreasing the long-wavelength detection light LW.

The light shielding film 2 is required to have an optical density (ODvalue) to ArF exposure light of 2.5 or more, and preferably 2.8 or more.When the optical density is less than 2.5, the property of shielding ArFexposure light becomes insufficient, and when exposure is performedusing a transfer mask using this mask blank, there occurs a problem ofcontrast of a projected optical image (transfer image) of the transfermask that is likely to be insufficient. On the other hand, to make thelight shielding film 2 thinner, the optical density of the lightshielding film 2 is preferably 4.0 or less.

The light shielding film 2 is required to have a surface reflectance(reflectance of a surface on a side opposite to the transparentsubstrate 1 side) to ArF exposure light of 40% or less, and preferably38% or less. When the surface reflectance to ArF exposure light ishigher than 40%, there occurs a problem of reflection of exposure lightthat becomes too large, and leads to deterioration of a projectedoptical image during transfer by exposure.

Additionally, the light shielding film 2 preferably has the surfacereflectance to ArF exposure light of 20% or more. This is because whenthe surface reflectance to ArF exposure light is less than 20%, patterninspection sensitivity during mask pattern inspection using light havinga wavelength of 193 nm or about 193 nm decreases.

The light shielding film 2 is required to have a back-surfacereflectance (reflectance of a surface on the transparent substrate 1side) to ArF exposure light of 40% or less, and preferably 35% or less.When the back-surface reflectance to ArF exposure light is more than40%, there occurs a problem of reflection of exposure light that becomestoo large, and leads to deterioration of a projected optical imageduring transfer by exposure.

To make the optical density, the surface reflectance, and theback-surface reflectance to ArF exposure light of the light shieldingfilm 2 within the aforementioned ranges, the light shielding film 2 hasa refractive index n to ArF exposure light of preferably 1.6 or more and2.1 or less, and more preferably 1.7 or more and 2.0 or less.Additionally, an extinction coefficient k to ArF exposure light ispreferably 1.6 or more and 2.1 or less, and more preferably 1.7 or moreand 2.0 or less.

The light shielding film 2 is required to have a transmittance to alight having a wavelength of 900 nm of 50% or less, and preferably 48%or less. The light shielding film 2 is required to have an extinctioncoefficient k to a light having a wavelength of 900 nm of 0.04 or more,and preferably 0.045 or more. Additionally, the extinction coefficient kto a light having a wavelength of 900 nm of the light shielding film 2is preferably 0.1 or less. The light shielding film 2 has a refractiveindex n to a light having a wavelength of 900 nm of preferably 2.5 ormore, and more preferably 2.7 or more. Additionally, the refractiveindex n to a light having a wavelength of 900 nm of the light shieldingfilm 2 is preferably 3.5 or less.

When the wavelength of a light is 800 nm or more and 900 nm or less, thelight shielding film 2 including the material containing silicon andnitrogen has properties in which the transmittance becomes higher andboth the refractive index n and the extinction coefficient k becomesmaller as the wavelength of the light becomes longer, as describedabove. Owing to these spectral properties, when a transmittance to alight having a wavelength of 900 nm is 50% or less and an extinctioncoefficient k to a light having a wavelength of 900 nm is 0.04 or more,the long-wavelength detection light LW having a wavelength in the rangeof 800 nm or more and 900 nm or less can be decreased sufficiently bythe light shielding film 2. Thus, the long-wavelength detection light LWcan be used to detect with sufficient contrast an alignment mark formedon a transfer mask manufactured using this mask blank. Accordingly, theproblem of exposure that cannot be performed owing to insufficientdetection sensitivity in alignment mark detection can be solved.

On the other hand, the light shielding film 2 has a transmittance to alight having a wavelength of 700 nm of preferably 45% or less, and morepreferably 40% or less. The light shielding film 2 has an extinctioncoefficient k to a light having a wavelength of 700 nm of preferably0.10 or more, and more preferably 0.15 or more. Additionally, theextinction coefficient k to a light having a wavelength of 700 nm of thelight shielding film 2 is preferably 0.5 or less. Additionally, thelight shielding film 2 has a refractive index n to a light having awavelength of 700 nm of preferably 2.8 or more, and more preferably 3.0or more. Additionally, the refractive index n to a light having awavelength of 700 nm of the light shielding film 2 is preferably 3.8 orless.

Depending on the exposure apparatus, an identification mark such as abar code formed on a transfer mask is read out using detection lighthaving a wavelength of less than 800 nm (e.g., a wavelength in the rangefrom 600 nm to 700 nm). In a transfer mask manufactured using a maskblank including the light shielding film 2 having the aforementionedoptical properties to a light having a wavelength of 700 nm, anidentification code can be read out reliably using the aforementioneddetection light having a wavelength of less than 800 nm.

The refractive index n and the extinction coefficient k of a thin filmare not determined by composition of the thin film alone. The filmdensity, crystal state and the like of the thin film are also elementsinfluencing the refractive index n and the extinction coefficient k.Therefore, conditions under which the light shielding film 2 is formedby reactive sputtering are adjusted to form the light shielding film 2having a desired refractive index n and a desired extinction coefficientk to make the optical density (OD value), the back-surface reflectance,and the surface reflectance to ArF exposure light, and the extinctioncoefficient k to a light having a wavelength of 900 nm fall within thespecified values. A way to make the refractive index n and theextinction coefficient k of the light shielding film 2 fall within theaforementioned specified range is not limited to adjustment of the ratioof the noble gas and the reactive gas in a mixed gas used in filmformation performed by reactive sputtering. There are various ways tomake the refractive index n and the extinction coefficient k of thelight shielding film 2 fall within the aforementioned specified range,including adjustment of a pressure within the film forming chamber infilm formation performed by reactive sputtering, adjustment of electricpower applied to a target, and adjustment of the positional relationshipsuch as the distance between the target and the transparent substrate.Additionally, these film forming conditions are specific to the filmforming device and are adjusted appropriately to form the lightshielding film 2 having a desired refractive index n and a desiredextinction coefficient k.

The light shielding film 2 is a single layer film in which thecomposition of a layer is even in a thickness direction of the layer orgradient in a thickness direction of the layer, except for a surfacelayer undergoing natural oxidation. The light shielding film 2 is asingle layer film and thus, the number of steps in manufacturingdecreases, production efficiency increases, and control of manufacturingquality including defects is facilitated.

A film not positively containing oxygen and containing silicon andnitrogen has high light fastness to ArF exposure light, but tends tohave lower chemical resistance than a film positively containing oxygen,and containing silicon and nitrogen. Additionally, in the case of themask blank 100 using the light shielding film 2 not positivelycontaining oxygen as the surface layer on the side opposite to thetransparent substrate 1 side of the light shielding film 2, it isdifficult to avoid oxidation of the surface layer of the light shieldingfilm 2 by washing a transfer mask 200 produced from the mask blank 100or storing the transfer mask 200 in air. When the surface layer of thelight shielding film 2 undergoes oxidation, there occurs a problem ofvariation in the surface reflectance to ArF exposure light of the lightshielding film 2, and variation in the transfer property by exposure ofthe transfer mask 200.

Thus, it is preferable that the surface layer on the side opposite tothe transparent substrate 1 side of the light shielding film 2positively contain oxygen. However, when all the light shielding film 2contains oxygen, there occurs a problem of decrease in a property ofshielding ArF exposure light and a property of decreasing thelong-wavelength detection light LW, as described above.

Therefore, it is desirable that the light shielding film 2 include onthe surface layer a composition gradient portion with increased oxygencontent toward a surface opposite to the transparent substrate 1, and aportion except for the surface layer in the light shielding film 2 (abulk portion of the light shielding film 2) be formed of the materialcontaining silicon and nitrogen. Here, the material containing siliconand nitrogen constituting the bulk portion of the light shielding film 2refers to a material consisting of silicon and nitrogen or a materialconsisting of silicon, nitrogen, and one or more elements selected froma semimetal element and a non-metal element. Note that in this case, anyof the refractive index n and the extinction coefficient k for the ArFexposure light of the light shielding film 2 is a value of all the lightshielding film 2 including the surface layer, and the extinctioncoefficient k to a light having a wavelength of 900 nm is also a valueof all the light shielding film 2 including the surface layer.

The light shielding film 2 is formed by sputtering, and any type ofsputtering such as DC sputtering, RF sputtering, and ion beam sputteringis applicable. When a target having low conductivity (such as a silicontarget, a silicon compound target containing no semimetal element or alittle amount of a semimetal element, and the like) is used, RFsputtering or ion beam sputtering is preferably applied, and RFsputtering is more preferably applied from the viewpoint of a filmforming rate.

A method of manufacturing the mask blank 100 is preferably a methodincluding forming the light shielding film 2 on the transparentsubstrate 1 by reactive sputtering in a sputtering gas containingnitrogen-based gas and the noble gas with use of a silicon target or atarget made of a material containing silicon and one or more elementsselected from a semimetal element and a non-metal element.

As the nitrogen-based gas used in the step of forming the lightshielding film, any gas is applicable as long as the gas is a gascontaining nitrogen. As described above, the light shielding film 2except for the surface layer preferably has a low oxygen content.Therefore, nitrogen-based gas containing no oxygen is preferablyapplied, and nitrogen gas (N₂ gas) is more preferably applied.Additionally, as the noble gas used in the step of forming the lightshielding film 2, any noble gas is applicable. Preferable examples ofthe noble gas include argon, krypton, and xenon. Additionally, to relaxa stress of a thin film, helium and neon having a small atomic weightcan be incorporated positively in the thin film.

Examples of a method of forming the light shielding film 2 including thecomposition gradient portion with increased oxygen content toward thesurface opposite to the transparent substrate 1 include a methodincluding gradually adding an oxygen gas as an atmospheric gas in afinal stage of forming the light shielding film 2 by sputtering, and amethod in which after the light shielding film 2 is formed bysputtering, post treatment such as heating treatment in a gas containingoxygen such as air, light irradiation treatment using a flash lamp orthe like in a gas containing oxygen such as air, and treatment ofbringing a surface of the light shielding film into contact with ozoneor oxygen plasma are added.

On the other hand, when it is preferable that the surface reflectance toArF exposure light of the light shielding film be made lower (e.g., 30%or less), the light shielding film with the aforementioned single layerstructure needs to contain a larger amount of nitrogen to achieve such asurface reflectance. In this case, an optical density per unit filmthickness of the light shielding film decreases, and to securepredetermined light shielding performance, it is necessary to increase afilm thickness of the light shielding film. In the case where such a lowsurface reflectance is required, it is preferable that the lightshielding film include a layered structure including a lower layer andan upper layer from the transparent substrate side, the lower layer beformed of a material for the light shielding film with a single layerstructure in the aforementioned embodiment, and the upper layer beformed of a material containing silicon and oxygen.

That is, a mask blank in another mode includes a light shielding film ona transparent substrate. The light shielding film includes a structurein which a lower layer and an upper layer are layered one on another inorder from the transparent substrate side. The lower layer is formed ofa material containing silicon and nitrogen, and the upper layer isformed of a material containing silicon and oxygen. The light shieldingfilm has an optical density to ArF exposure light of 2.5 or more, asurface reflectance to ArF exposure light of 30% or less, a back-surfacereflectance to ArF exposure light of 40% or less, and a transmittance toa light having a wavelength of 900 nm of 50% or less. The lower layer ofthe light shielding film has an extinction coefficient k of 0.04 or moreto a light having a wavelength of 900 nm. The light shielding film has athickness of 60 nm or less.

Additionally, in this mask blank in another mode, it is preferable thatthe lower layer of the light shielding film be formed of a materialconsisting of silicon and nitrogen, or a material consisting of silicon,nitrogen, and one or more elements selected from a semimetal element anda non-metal element. Further, in this mask blank in another mode, it ispreferable that the upper layer of the light shielding film be formed ofa material consisting of silicon and oxygen, or a material consisting ofsilicon, nitrogen, and one or more elements selected from a semimetalelement and a non-metal element. Specifically, the lower layer of thelight shielding film includes the same configuration as theconfiguration of the light shielding film with a single layer structurein the aforementioned embodiment.

The upper layer has an extinction coefficient k to a light having awavelength of 800 nm or more and 900 nm or less of approximately 0, andthe upper layer can hardly contribute to shielding of light having sucha wavelength. Therefore, it is preferable that light shieldingperformance to a light having a wavelength of 800 nm or more and 900 nmor less be secured by the lower layer of the light shielding film alone.Additionally, the upper layer is required to have a function to reducethe surface reflectance, and thus the upper layer has low lightshielding performance to ArF exposure light. Therefore, it is preferablethat a predetermined optical density to ArF exposure light be secured bythe lower layer of the light shielding film alone.

A transfer mask in another mode includes a light shielding filmincluding a transfer pattern on a transparent substrate. The lightshielding film includes a structure in which a lower layer and an upperlayer are layered one on another in order from the transparent substrateside. The lower layer is formed of a material containing silicon andnitrogen, and the upper layer is formed of a material containing siliconand oxygen. The light shielding film has an optical density to ArFexposure light of 2.5 or more, a surface reflectance to ArF exposurelight of 30% or less, a back-surface reflectance to ArF exposure lightof 40% or less, and a transmittance to a light having a wavelength of900 nm of 50% or less. The lower layer of the light shielding film hasan extinction coefficient k to a light having a wavelength of 900 nm of0.04 or more. The light shielding film has a thickness of 60 nm or less.Note that other matters (matters relating to the transparent substrateand a hard mask film, and the like) according to the mask blank and thetransfer mask in another mode are the same as those of the mask blankand the transfer mask in the aforementioned embodiment.

Hard Mask Film

In the mask blank 100 including the light shielding film 2, it ispreferable that a hard mask film 3 formed of a material having etchingselectivity to an etching gas used in etching the light shielding film 2be further layered on the light shielding film 2. Since the lightshielding film 2 needs to ensure a predetermined optical density, thelight shielding film 2 has a lower limit of the thickness. The hard maskfilm 3 has a film thickness sufficient to be capable of functioning asan etching mask until the end of dry etching for forming a pattern onthe light shielding film 2 located immediately under the hard mask film3, and the thickness of the hard mask film 3 is not basically limited byoptical properties. Therefore, the hard mask film 3 can have a thicknesssignificantly smaller than the thickness of the light shielding film 2.Then, since a resist film made of an organic material has a filmthickness sufficient to function as an etching mask until the end of dryetching for forming a pattern on this hard mask film 3, the resist filmcan have the thickness significantly smaller than the thickness of aknown resist film, and the problem such as resist pattern collapse canbe suppressed.

The hard mask film 3 is preferably formed of a chromium (Cr)-containingmaterial. The chromium-containing material has particularly high dryetching durability to dry etching using fluorine-based gas such as SF₆.

When the chromium-containing material is used for the light shieldingfilm 2, the film thickness of the light shielding film 2 is relativelylarge. Thus, a problem of side etching occurs during dry etching of thelight shielding film 2. However, when the chromium-containing materialis used for the hard mask film 3, the film thickness of the hard maskfilm 3 is relatively small. Thus, a problem due to side etching is lesslikely to occur.

Examples of the chromium-containing material include a chrome metal anda material containing one or more elements incorporated in chromium andselected from oxygen, nitrogen, carbon, boron, and fluorine, such asCrN, CrC, CrON, CrCO, and CrCON. A film made of a material containingthese elements added to the chrome metal is likely to be a film with anamorphous structure. Surface roughness of the film and line edgeroughness in dry etching of the light shielding film 2 are suppressed.Thus, such a film is preferable.

Additionally, from the viewpoint of dry etching of the hard mask film 3,a material containing one or more elements incorporated in chromium andselected from oxygen, nitrogen, carbon, boron, and fluorine ispreferably used as a material forming the hard mask film 3.

A chromium-based material is etched with a mixed gas of chlorine-basedgas and oxygen gas. However, a chromium metal has an etching raterelatively low for this etching gas. One or more elements selected fromoxygen, nitrogen, carbon, boron, and fluorine can be incorporated inchromium to enhance the etching rate for the etching mixed gas ofchlorine-based gas and oxygen gas. Additionally, the chromium-containingmaterial forming the hard mask film 3 may contain one or more elementsof indium, molybdenum, or tin. The chromium-containing material formingthe hard mask film 3 contains one or more elements of indium,molybdenum, or tin and thus, the etching rate for a mixed gas ofchlorine-based gas and oxygen gas can be further enhanced.

As a material forming the hard mask film 3 other than thechromium-containing material, a metal such as tantalum (Ta) and tungsten(W), or a material containing a metal such as tantalum is alsoapplicable. In this case, examples of the material containing tantaluminclude a tantalum metal, and a material containing one or more elementsincorporated in tantalum and selected from nitrogen, boron, and carbon.Specific examples thereof include Ta, TaN, TaO, TaON, TaBN, TaBO, TaBON,TaCN, TaCO, TaCON, TaBCN, and TaBOCN.

In the mask blank 100, a resist film made of an organic material andhaving a film thickness of 100 nm or less is preferably formed incontact with a surface of the hard mask film 3. In the case of a finepattern supporting the hp 32 nm generation of DRAMs, a Sub-ResolutionAssist Feature (SRAF) having a line width of 40 nm may be provided on atransfer pattern to be formed on the hard mask film 3. However, sinceeven in such a case, an aspect ratio of a cross section of a resistpattern can be as low as 1:2.5, collapsing or peeling off of the resistpattern during development, rinsing, or the like of the resist film canbe suppressed. Note that the resist film more preferably has a filmthickness of 80 nm or less.

In the mask blank 100, a resist film can also be formed directly incontact with the light shielding film 2 without the hard mask film 3being provided. In this case, the mask blank 100 includes a simplestructure and dry etching of the hard mask film 3 becomes unnecessarywhen a transfer mask is manufactured. Therefore, the number of steps inmanufacturing can be reduced. Note that in this case, the resist film ispreferably formed after the light shielding film 2 is subjected tosurface treatment using hexamethyldisilazane (HMDS) or the like.

Additionally, the mask blank of the present disclosure is a mask blanksuitable for application of a binary mask, as described below. However,the mask blank is not limited to the application of a binary mask. Themask blank can be used as a mask blank for a Levenson phase shift maskor a mask blank for a Chromeless Phase Lithography (CPL) mask.

Transfer Mask

FIGS. 4A to 4F are schematic cross-sectional views illustrating steps inmanufacturing the transfer mask (binary mask) 200 from the mask blank100 according to the embodiment of the present disclosure.

The transfer mask 200 in the embodiment of the present disclosure is abinary mask including the light shielding film 2 having a transferpattern (light shielding film pattern 2 a) on the transparent substrate1. The light shielding film is a single layer film formed of a materialcontaining silicon and nitrogen, and has an optical density to an ArFexcimer laser exposure light of 2.5 or more, a surface reflectance tothe exposure light of 40% or less, and a back-surface reflectance to theexposure light of 40% or less, a transmittance to a light having awavelength of 900 nm of 50% or less, an extinction coefficient to alight having a wavelength of 900 nm of 0.04 or more, and a thickness of60 nm or less.

Matters relating to the transparent substrate 1 and the light shieldingfilm 2 in the transfer mask 200 are the same as those in the mask blank100, and the transfer mask 200 has the same technical features as thoseof the mask blank 100.

Additionally, in a method of manufacturing the transfer mask 200 of thepresent disclosure, the aforementioned mask blank 100 is used. Themethod includes the steps of forming a pattern including a transferpattern and an alignment mark on the hard mask film 3 by dry etching,forming a pattern including a transfer pattern and an alignment mark onthe light shielding film 2 by dry etching using the hard mask film 3having the pattern (hard mask pattern 3 a) as a mask, and removing thehard mask pattern 3 a.

In such a transfer mask 200, even when an exposure apparatus configuredto perform alignment using the long-wavelength detection light LW isused, an alignment mark can be detected with sufficient contrast. Thus,an alignment operation can be executed without causing an error.

In addition, the transfer mask 200 has high ArF light fastness, and evenin the case of the transfer mask 200 obtained after cumulativeirradiation with exposure light of an ArF excimer laser, a CriticalDimension (CD) change (increase) of the light shielding film pattern 2 acan be suppressed to fall within a small range.

Thus, the transfer mask 200 is placed on a mask stage of an exposureapparatus using an ArF excimer laser as exposure light and configured toperform alignment using the long-wavelength detection light LW. Evenwhen the light shielding film pattern 2 a is transferred by exposure toa resist film, a pattern can be transferred to the resist film on asemiconductor device with precision sufficiently satisfying designspecification in association with a mask alignment operation.

Hereinafter, the method of manufacturing the transfer mask 200 will bedescribed as an example according to the steps in manufacturingillustrated in FIGS. 4A to 4F. Note that in this example, a materialcontaining silicon and nitrogen is applied to the light shielding film 2and a chromium-containing material is applied to the hard mask film 3.

First, the mask blank 100 (see FIG. 4A) is prepared and a resist film isformed in contact with the hard mask film 3 using a spin coating method.Next, the pattern to be formed on the light shielding film 2 isexposure-drawn and a predetermined treatment such as a developmenttreatment is further performed to form a resist pattern 4 a (see FIG.4B). Note that the pattern written by an electron beam includes atransfer pattern and an alignment mark.

Subsequently, dry etching using chlorine-based gas such as a mixed gasof chlorine and oxygen and using the resist pattern 4 a as a mask isperformed to form a pattern (hard mask pattern 3 a) on the hard maskfilm 3 (see FIG. 4C). The chlorine-based gas is not particularly limitedas long as the chlorine-based gas contains Cl. Examples of thechlorine-based gas can include Cl₂, SiCl₂, CHCl₃, CH₂Cl₂, and BCl₃. Whenthe mixed gas of chlorine and oxygen is used, a flow rate ratio of thegas may be, for example, Cl₂:O₂=4:1.

Next, the resist pattern 4 a is removed by ashing or using a resiststripper (see FIG. 4D).

Subsequently, dry etching using fluorine-based gas and using the hardmask pattern 3 a as a mask is performed to form a pattern (lightshielding film pattern 2 a) on the light shielding film 2 (see FIG. 4E).As the fluorine-based gas, any gas containing F can be used, and SF₆ isfavorable. In addition to SF₆, examples of the fluorine-based gas caninclude CHF₃, CF₄, C₂F₆, and C₄F₈. Fluorine-based gas containing C has arelatively high etching rate for the transparent substrate 1 made of aglass material. Since SF₆ causes small damage to the transparentsubstrate 1, SF₆ is preferable. Note that He or the like may further beadded to SF₆.

Thereafter, the hard mask pattern 3 a is removed using a chromiumetching liquid and a predetermined treatment such as washing isperformed to obtain the transfer mask 200 (see FIG. 4F). Note that inthe step of removing the hard mask pattern 3 a, dry etching using amixed gas of chlorine and oxygen may be performed. Here, an example ofthe chromium etching liquid can include a mixture containing diammoniumcerium nitrate and perchloric acid.

Note that the case where the transfer mask 200 is a binary mask isdescribed here; however, the transfer mask of the present disclosure isnot limited to a binary mask and can be applied to a Levenson phaseshift mask or a CPL mask. That is, when the transfer mask is a Levensonphase shift mask, the light shielding film of the present disclosure canbe used for a light shielding film of the transfer mask. Additionally,when the transfer mask is a CPL mask, the light shielding film of thepresent disclosure can be used at a region mainly including an outercircumferential light shielding band. Then, as with the case of thebinary mask, in the case of a Levenson phase shift mask and a CPL mask,alignment mark detection can be performed using the long-wavelengthdetection light LW with sufficient contrast.

Further, a method of manufacturing a semiconductor device of the presentdisclosure includes transferring by exposure a pattern to a resist filmon a semiconductor substrate using the aforementioned transfer mask 200or the transfer mask 200 manufactured using the aforementioned maskblank 100.

The transfer mask 200 and the mask blank 100 of the present disclosurehave the effects as described above. Therefore, when the transfer maskof the present disclosure is used to perform exposure on a resist filmformed on a semiconductor wafer, alignment mark detection can beperformed with sufficient sensitivity.

Therefore, a semiconductor device can be manufactured without anexposure operation stop associated with insufficient alignment markdetection sensitivity and with high ArF light fastness.

EXAMPLES

Hereinafter, embodiments of the present disclosure will be describedmore specifically by way of examples.

Example 1 Manufacture of Mask Blank

A transparent substrate 1 having a main surface dimension ofapproximately 152 mm×approximately 152 mm and including synthetic quartzglass having a thickness of approximately 6.25 mm was prepared. An endsurface and a main surface of this transparent substrate 1 were polishedto obtain predetermined surface roughness and then subjected topredetermined washing treatment and drying treatment.

Next, the transparent substrate 1 was installed in a single-wafer RFsputtering apparatus, and a light shielding film 2 including silicon andnitrogen (Si:N=50 atom %:50 atom %) was formed to have a thickness of 57nm on the transparent substrate 1 by reactive sputtering (RF sputtering)using a silicon (Si) target and a mixed gas of krypton (Kr), helium(He), and nitrogen (N₂) (flow rate ratio Kr:He:N₂=10:100:1, pressure:0.1 Pa) as a sputtering gas at an electric power of a RF power supply of1.5 kW. Here, the composition of the light shielding film 2 is of aresult obtained by measurement by an X-ray photoelectron spectroscopy(XPS). Hereinafter, a method of measuring film compositions of otherfilms is similar to the aforementioned method.

Next, the transparent substrate 1 on which the light shielding film 2was formed was subjected to heating treatment under conditions of aheating temperature of 500° C. and treatment time of 1 hour in air toadjust a stress of the film. FIG. 2 shows a result obtained using aspectrophotometer (Cary4000 manufactured by Agilent Technologies) tomeasure a spectral transmission of the light shielding film 2 obtainedafter the heating treatment. A transmittance to a long-wavelength lighthaving a wavelength of 800 nm or more and 900 nm or less monotonicallyincreases as the wavelength is longer. The transmittances at wavelengthsof 800 nm, 850 nm, 890 nm, and 900 nm were 42.8%, 44.9%, 46.7%, and47.0%, respectively. Additionally, an optical density (OD value) to anArF excimer laser light (wavelength: 193 nm) was 2.96.

Additionally, a refractive index n and an extinction coefficient k ofthe light shielding film 2 were measured using a spectroscopicellipsometer (M-200D available from J. A. Woollam Co., Inc.). FIG. 3shows spectral properties of the light shielding film 2, that is,measurement results of the refractive index n and the extinctioncoefficient k at each wavelength. The refractive index n at a wavelengthof 193 nm was 1.830 and the extinction coefficient k at a wavelength of193 nm was 1.785. The refractive index n at a wavelength of 800 nm was3.172 and the extinction coefficient k at a wavelength of 800 nm was0.093. The refractive index n at a wavelength of 850 nm was 3.137 andthe extinction coefficient k at a wavelength of 850 nm was 0.066. Therefractive index n at a wavelength of 890 nm was 3.112 and theextinction coefficient k at a wavelength of 890 nm was 0.050. Therefractive index n at a wavelength of 900 nm was 3.106 and theextinction coefficient k at a wavelength of 900 nm was 0.047.

A surface reflectance and a back-surface reflectance of the lightshielding film 2 at a wavelength of 193 nm were measured using aspectrophotometer (U-4100 available from Hitachi High-TechnologiesCorporation), and values of the surface reflectance and the back-surfacereflectance were 37.1% and 30.0%, respectively.

Next, the transparent substrate 1 on which the light shielding film 2obtained after the heating treatment was formed was installed in asingle-wafer DC sputtering device, and a hard mask film 3 including aCrN film having a film thickness of 5 nm was formed by reactivesputtering (DC sputtering) using a chromium (Cr) target in an atmosphereof a mixed gas of argon (Ar) and nitrogen (N₂). A film composition ratioof this film was measured by XPS, and had Cr of 75 atom % and N of 25atom %. Then, heat treatment was performed at a temperature (280° C.)lower than the temperature in the heating treatment performed on thelight shielding film 2 and a stress of the hard mask film 3 wasadjusted.

A mask blank 100 including a structure in which the light shielding film2 and the hard mask film 3 were layered on the transparent substrate 1was manufactured by the aforementioned procedure.

Manufacture of Transfer Mask

Next, a transfer mask (binary mask) 200 in Example 1 was produced by thefollowing procedure with use of the mask blank 100 in Example 1.

First, the mask blank 100 in Example 1 (see FIG. 4A) was prepared. Aresist film including a chemically amplified resist for electron beamlithography and having a film thickness of 80 nm was formed in contactwith a surface of the hard mask film 3. Next, a pattern to be formed onthe light shielding film 2 was written by an electron beam on the resistfilm and predetermined development treatment and washing treatment wereperformed to form a resist pattern 4 a (see FIG. 4B). Note that thepattern written by an electron beam includes a transfer pattern and analignment mark.

Next, dry etching using a mixed gas of chlorine and oxygen (gas flowrate ratio Cl₂:O₂=4:1) was performed using the resist pattern 4 a as amask, to form a pattern (hard mask pattern 3 a) on the hard mask film 3(see FIG. 4C).

Next, the resist pattern 4 a was removed (see FIG. 4D). Subsequently,dry etching using fluorine-based gas (mixed gas of SF₆ and He) wasperformed using the hard mask pattern 3 a as a mask, to form a pattern(light shielding film pattern 2 a) on the light shielding film 2 (seeFIG. 4E).

Thereafter, the hard mask pattern 3 a was removed using a chromiumetching liquid containing diammonium cerium nitrate and perchloric acidand was subjected to predetermined treatment such as washing to obtainthe transfer mask 200 (see FIG. 4F).

The transfer mask 200 manufactured in Example 1 was placed in anexposure apparatus using long-wavelength detection light LW, andalignment mark detection was performed. At that time, the mark detectionwas able to be performed with sufficient contrast. Then, a maskalignment operation was able to be executed without causing any error.

Next, the transfer mask 200 was subjected to intermittent irradiationtreatment with an ArF excimer laser beam at a cumulative irradiationamount of 40 kJ/cm². An amount of change in CD of the light shieldingfilm pattern 2 a before and after this irradiation treatment was 1.2 nmor less, and was an amount of change in CD falling within the rangeusable as the light shielding film pattern 2 a. Thus, it was found thatthe light shielding film pattern 2 a has sufficient ArF light fastnessin practical terms.

The transfer mask 200 in Example 1 was placed on a mask stage of theexposure apparatus, and exposure-transferred on a resist film on asemiconductor device. As a result, a circuit pattern was able to beformed with high precision without causing mask alignment failure.

Comparison Example 1 Manufacture of Mask Blank

A mask blank in Comparative Example 1 was manufactured by the sameprocedure as the procedure for the mask blank 100 in Example 1 exceptthat a light shielding film was formed as follows.

The method of forming a light shielding film in Comparative Example 1 isas follows. A transparent substrate 1 was installed in a single-wafer RFsputtering device. A light shielding film including silicon and nitrogen(Si:N=48 atom %:52 atom %) and having a thickness of 100 nm was formedon the transparent substrate 1 by reactive sputtering (RF sputtering)using a silicon (Si) target and using a mixed gas of krypton (Kr),helium (He), and nitrogen (N₂) as a sputtering gas.

Next, the transparent substrate 1 on which the light shielding film wasformed was subjected to heating treatment under conditions of a heatingtemperature of 500° C. and treatment time of 1 hour in air to adjust thestress of the film. A spectral transmission of the light shielding filmobtained after the heating treatment was measured by a spectrophotometer(Cary4000 available from Agilent Technologies). As a result, thetransmittances at wavelengths of 800 nm, 850 nm, 890 nm, and 900 nm were74.2%, 74.2%, 73.9%, and 73.9%, respectively. Additionally, an opticaldensity (OD value) to an ArF excimer laser beam (wavelength: 193 nm) was2.9.

Additionally, a refractive index n and an extinction coefficient k ofthe light shielding film were measured using a spectroscopicellipsometer (M-200D available from J. A. Woollam Co., Inc.). Therefractive index n at a wavelength of 193 nm was 2.4 and the extinctioncoefficient k at a wavelength of 193 nm was 1.0. The refractive index nat a wavelength of 800 nm was 2.3 and the extinction coefficient k at awavelength of 800 nm was 0. The refractive index n at a wavelength of850 nm was 2.3 and the extinction coefficient k at a wavelength of 850nm was 0. The refractive index n at a wavelength of 890 nm was 2.3 andthe extinction coefficient k at a wavelength of 890 nm was 0. Therefractive index n at a wavelength of 900 nm was 2.3 and the extinctioncoefficient k at a wavelength of 900 nm was 0.

A surface reflectance and a back-surface reflectance of the lightshielding film at a wavelength of 193 nm were measured using aspectrophotometer (U-4100 available from Hitachi High-TechnologiesCorporation), and values of the surface reflectance and the back-surfacereflectance were 21% and 15%, respectively.

Manufacture of Transfer Mask

Next, a transfer mask (binary mask) in Comparative Example 1 wasmanufactured by the same procedure as in Example 1 with use of the maskblank in Comparative Example 1.

The manufactured transfer mask in Comparative Example 1 was placed in anexposure apparatus using long-wavelength detection light LW, andalignment mark detection was performed. At that time, the mark detectioncould not be performed with sufficient contrast. Then, a mask alignmenterror was often caused.

Next, the transfer mask in Comparative Example 1 was subjected tointermittent irradiation treatment with an ArF excimer laser beam at acumulative irradiation amount of 40 kJ/cm². An amount of change in CD ofthe light shielding film pattern before and after this irradiationtreatment was 1.2 nm or less, and was an amount of change in CD fallingwithin the range usable as the light shielding film pattern. The lightshielding film pattern had sufficient ArF light fastness in practicalterms.

The transfer mask 200 in Comparative Example 1 was placed on a maskstage of the exposure apparatus, and exposure-transferred on a resistfilm on a semiconductor device. At that time, a mask alignment failureoften occurred, and stable exposure for manufacturing a semiconductordevice could not be performed.

REFERENCE SIGNS LIST

-   1 Transparent substrate-   2 Light shielding film-   2 a Light shielding film pattern-   3 Hard mask film-   3 a Hard mask pattern-   4 a Resist pattern-   100 Mask blank-   200 Transfer mask (binary mask)

1. A mask blank comprising a light shielding film on a transparentsubstrate; wherein the light shielding film is a single-layer filmcontaining silicon and nitrogen; wherein a refractive index n of thelight shielding film to an exposure light of an Arf excimer laser is 1.6or more and 2.1 or less; wherein an extinction coefficient k of thelight shielding film to the exposure light is 1.6 or more and 2.1 orless; wherein an extinction coefficient k of the light shielding film toa light having a wavelength of 900 nm is 0.04 or more; and wherein athickness of the light shielding film is 40 nm or more and 60 nm orless.
 2. The mask blank according to claim 1, wherein a refractive indexn of the light shielding film to a light having a wavelength of 900 nmis 3.5 or less.
 3. The mask blank according to claim 1, wherein anextinction coefficient k of the light shielding film to a light having awavelength of 700 nm is 0.10 or more.
 4. The mask blank according toclaim 1, wherein a refractive index n of the light shielding film to alight having a wavelength of 700 nm is 3.8 or less.
 5. The mask blankaccording to claim 1, wherein the light shielding film consists ofsilicon and nitrogen, or consists of silicon, nitrogen, and one or moreelements selected from a semimetal element and a non-metal element. 6.The mask blank according to claim 1, wherein the light shielding filmcomprises at its surface layer a composition gradient portion withincreased oxygen content toward a surface opposite to the transparentsubstrate, and the light shielding film except for the surface layerconsists of silicon and nitrogen, or consists of silicon, nitrogen, andone or more elements selected from a semimetal element and a non-metalelement.
 7. The mask blank according to claim 1, wherein nitrogencontent of the light shielding film is 50 atom % or less.
 8. The maskblank according to claim 1, wherein silicon content of the lightshielding film is 50 atom % or more.
 9. The mask blank according toclaim 1, wherein a hard mask film containing chromium is provided on thelight shielding film.
 10. A transfer mask comprising on a transparentsubstrate a light shielding film including a transfer pattern; whereinthe light shielding film is a single-layer film containing silicon andnitrogen; wherein a refractive index n of the light shielding film to anexposure light of an Arf excimer laser is 1.6 or more and 2.1 or less;wherein an extinction coefficient k of the light shielding film to theexposure light is 1.6 or more and 2.1 or less; wherein an extinctioncoefficient k of the light shielding film to a light having a wavelengthof 900 nm is 0.04 or more; and wherein a thickness of the lightshielding film is 40 nm or more and 60 nm or less.
 11. The transfer maskaccording to claim 10, wherein a refractive index n of the lightshielding film to a light having a wavelength of 900 nm is 3.5 or less.12. The transfer mask according to claim 10, wherein an extinctioncoefficient k of the light shielding film to a light having a wavelengthof 700 nm is 0.10 or more.
 13. The transfer mask according to claim 10,wherein a refractive index n of the light shielding film to a lighthaving a wavelength of 700 nm is 3.8 or less.
 14. The transfer maskaccording to claim 10, wherein the light shielding film consists ofsilicon and nitrogen, or consists of silicon, nitrogen, and one or moreelements selected from a semimetal element and a non-metal element. 15.The transfer mask according to claim 10, wherein the light shieldingfilm comprises at its surface layer a composition gradient portion withincreased oxygen content toward a surface opposite to the transparentsubstrate, and the light shielding film except for the surface layerconsists of silicon and nitrogen, or consists of silicon, nitrogen, andone or more elements selected from a semimetal element and a non-metalelement.
 16. The transfer mask according to claim 10, wherein nitrogencontent of the light shielding film is 50 atom % or less.
 17. Thetransfer mask according to claim 10, wherein silicon content of thelight shielding film is 50 atom % or more.
 18. A method of manufacturinga semiconductor device, the method comprising the step ofexposure-transferring a transfer pattern on a resist film on asemiconductor substrate using the transfer mask according to claim 10.